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Variation in microneedle geometry to increase shear strength

Elsevier Ltd
Publication Date
DOI: 10.1016/j.proeng.2010.09.272
  • Microneedles
  • Drie
  • Microfluidics
  • Lab-On-A-Chip
  • Bio-Mems
  • Mathematics


Abstract This research aims to validate the effect of geometrical variations on the fracture strength of hollow silicon microneedles. Needle failure due to axial and shear loads may be due to heterogeneous peak stresses within the bulk material. Analytical determination of physical usage limits of microneedles can be misleading, as beam fracture models do not translate well to the micro-scale. Needle failure due to breakage can generally attributed to shear forces. In the study, 35 and 36 gauge hollow microneedles with a conventional circular lumen and those with enhanced ‘letter I’ shaped lumen geometry were fabricated. Due to their geometry, the ‘I’ shaped needles have a higher second moment of inertia, which leads to higher strength. The fracture limits of these needles due to shear forces were quantified. Average shear fracture limits of 36 gauge needles was 36.51 gf for circular geometry, while for the ‘I’ shaped needles it was 96.64 gf along the lateral direction. For 35 gauge needles the average fracture limits were 79.9 gf for circular needles, and 148.65 gf along the lateral direction for the enhanced geometry needles. Along the weaker axis, the enhanced geometry resulted in marginally lower strength than the circular counterparts for the 35 gauge needles, while it appreciably increased for the 36 gauge needles. The effect of geometry on shear strength was significantly higher for smaller microneedles.

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